Web coating control

ABSTRACT

The following specification describes an arrangement for applying a uniform oil coating of selected thickness to a steel web moving at variable speed past an absorbent roll which coats the web with oil. The roll travels the same distance as the web and drives a counter for counting a predetermined number of web lengths irrespective of web speed. A selected quantity of oil is sprayed on the roll under control of a timer after a predetermined number of web lengths are counted to ensure that the quantity of oil sprayed corresponds to a predetermined web length for providing a uniform oil coat of selected thickness irrespective of web speed.

United States Patent Inventor Henry J. Mozzi, Jr.

Chicago, Ill. Appl. No. 743,728 Filed July 10, 1968 Patented July 6, 1971 Assignee Stewart-Warner Corporation Chicago, Ill.

WEB COATING CONTROL 4 Claims, 6 Drawing Figs.

U.S. C1 118/8, 118/9, 118/259 Int. Cl B05c 11/02 Field of Search 118/7, 8, 9,

[56] References Cited UNITED STATES PATENTS 3.301.699 1/1967 Mozzi 117/111 Primary Examiner-John P. Mclntosh AuomeysAugustus G. Douvas and William J. Newman ABSTRACT: The following specification describes an arrangement for applying a uniform oil coating of selected thickness to a steel web moving at variable speed past an absorbent roll which coats the web with oil. The roll travels the same distance as the web and drives a counter for counting a predetermined number of web lengths irrespective of web speed. A selected quantity of oil is sprayed on the roll under control of a timer after a predetermined number of web lengths are counted to ensure that the quantity of oil sprayed corresponds to a predetermined web length for providing a uniform oil coat of selected thickness irrespective of web speed.

E n I INVENTOR HENRY J. MOZZI Jr.

PATENTEU JUL 61971 sum 1 BF 4 F u u n| PATENTEDJUL 6l97l 3590778 sum 2 OF 4 INVENTOR HENRY J.MOZZ| Jr.

PATENTEDJUL sum 3,590,778

sum 3 0r 4 INVE NTOR HENRY J. MOZZI Jr PATENTEU JUL 6 15m SHEET l [1F 4 SMI FIG.6.

INVENTOR HENRY J MOZZI Jr.

WEB COATING CONTROL BRIEF DESCRIPTION OF THE INVENTION FIELD OF THE INVENTION This invention relates to a system for coating webs and more particularly to the provision of an oil coating of desired thickness on a variable speed moving metal web.

BACKGROUND OF THE INVENTION In rolling mills steel sheet is passed between rollers which roll the sheet or web to a desired thickness and the sheet is then coiled. After the steel is rolled and before it is coiled, it is desirable to provide the sheet with an oil coat to avoid rusting and sometimes to provide a lubricating surface for subsequent operations. Oil coatings are required for metals other than steel, and coatings other than oil such as liquified waxes are also required for either steel or other metals; but, in any event, the coatings are usually required to be uniform and of a selected thickness.

An arrangement providing a uniform coating is shown in U.S. Pat. No. 3,301,699 issued Jan. 31, I967. In that patent a plurality of spray heads distributed across the width of the web are cyclically turned on and off in a desired sequence to spray an absorbent roll with oil which uniformly coats the web.

In this arrangement the thickness of the oil coating depends on the amount of oil provided by the absorbent roll per unit area of the web and this in turn depends both on the spray time for the oil and the web speed. One technique for controlling the coating thickness is disclosed in U.S. Pat. application Ser. No. 538,299 filed Mar. 29, 1966 by Gunter F. M.

Hoffmann now Pat. No. 3,416,489.

In this application a timing relay is periodically actuated by a rotating member keyed to the absorbent roll to spray oil on the roll for a time period determined by a clock setting. The web speed may range as high as 4,000 feet per minute to rotate the roll at approximately 2,000 rpm. depending on the roll diameter. With a SO-to-l gear reduction between the roll shaft and the rotating member, only about two-thirds of a second elapses between timing relay actuations, although the total or unit web length that passes the roll between timing relay actuations is constant irrespective of web speed. With a total cycle time of two-thirds of a second, the spray time could be not much longer than one-third of a second at high web speeds.

If the web started to slow, the one-third of a second spray time provided an excess amount of oil over the portion of the web passing the roll during that one-third of a second, since only a short web length passed during that time portion. During the remainder or dry portion of the cycle a greater web length passed the roll than during the corresponding dry portion when the web was running at high speed and therefore under oiling would occur towards the end of that web portion.

If, on the other hand, the web was running at, for example, 2,000 feet per minute and a total cycle time of l Ibseconds was available between timing relay actuations, the spray time could be increased correspondingly. Then, if the web was speeded up substantially, the spray time occurred while the a greater portion of the total web length passed theroll leaving an excess of oil for the portion of the web passing during the dry or off time of the spray.

The most versatile arrangement would be to have both the spray cycle and the dry or off cycle as short and as frequent as possible. Due to the finite conditions required to generate and terminate the spray, one-third of a second for the spray cycle is about the shortest practical cycle. Also, either a dry or wet cycle of very short duration could create too much percent variation in the total length per cycle if the spray output or web speed varied. With a relatively large ofi time the web length per cycle is increased andslight variations in spray output or web speed are not too critical.

Increasing the spray time is also desirable for many applications since as many as 3 to 6 seconds of spray time are needed, but this usually also requires a substantial increase in the off time or dry portion of'the web. Increasing the off time in a system of the type described required increased gear reduction, which is unnecessary for many systems so that gear reduction systems have to be tailored for different applications.

SUMMARY OF THE INVENTION In brief, the present invention utilizes counting "apparatus to count the passage of a desired number of web lengths to provide a constant web length irrespective of web speed during the dry or off portion of the cycle. The installation of the counting apparatus avoids the necessity to tailor the gear reduction for the needs of the system since it is inexpensive and is easily controlled to select any one of a wide variety of predetermined web lengths permitting in turn the selection of a wide variety of spray times. When a selected count is reached indicating the passage of a total predetermined web length, the spray is turned on under the control of a clock or timer to spray the web for a selected time. The counting apparatus is disabled during the spray so that the spray time can be varied within wide limits irrespective of web speed and since the web length passing the roll during the dry portion is constant, variations in web speed do not radically alter the coating thickness.

Accordingly, it is one object of the present invention to economically provide a more versatile system for coating a moving web with a coat of desired thickness.

It is another object of the present invention to provide an improved system or method for uniformly coating to a selected thickness with oil a metal web moving in a wide range of speeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view of a typical steel mill roll stand and a coating stand having coating apparatus employing the principles of the present invention;

FIG. 2 is an enlarged fragmentary section view of the relevant portion of the coating assembly;

FIG. 3 illustrates the flexible shaft connections between the coating roll and the pulse contact assembly;

FIG. 4 is an isometric view of the pulse contact assembly;

FIG. 5 is an isometric view of the instrument panel; and

FIG. 6 is a circuit diagram illustrating the circuits employed in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawings, a steel mill roll stand is indicated generally therein by the reference character 10. The stand comprises a rigid framework 12 supported on a concrete base 14 with the frame having a pair of vertical legs 16 on each side of a steel web 18 passing between the leg pairs.

Journal blocks 20 and 22 are located between the legs l6'on each side for rotatably supporting rollers 24 and 26 respectively for rolling the web 18 therebetween to a desired thickness. The axis of rollers 24 and 26 lie in a common vertical plane and the pressure under which they roll the web 18 is controlled bya pair of pressure rollers 28 and 30 under pressure supplied through a hydraulic cylinder assembly such as The web 18, after passing between the rollers 24 and 26, is supported by roller stand assemblies such as 34 spaced along a walkway 36 and is coated with oil by means of a coating assembly 38 andsubsequently coiled at a stand, not shown.

The coating assembly 38 comprises a conventional framework 40 straddling the web for adjustably supporting pairs of journal blocks such as 42 and 44. The journal blocks 42 and 44 are adjustable along the vertical axis of the framework. Journal block 42 rotatably supports a coating roller 46 of absorbent material such as described in the aforementioned US. Pat. No. 3,301,699 and adapted to engage one side of the web. Pressure on the rollers 46 and 48 is exerted along the vertical axis of the framework 40 by means of hydraulic assembly 50.

A housing or shroud 52 covers a peripheral portion of the coating roller 46 to prevent the general dissemination of oil fumes and a conduit 54 at the top of the shroud provides a controlled exit for the fumes. As seen in FIG. 2, oil to the roller 46 is supplied from a plurality of spray nozzles such as N1 and NX distributed axially along the roller 46 in respective rows on opposite sides of a vertical plane passing through the roller axis. It will be appreciated, of course, that the lower roll 48 can be an absorbent roll and the oil sprayed thereon.

The oil spray nozzles N1, etc., are supplied with oil from pumps through conduit 56 and each nozzle is controlled by a respective solenoid valve as SV] and SVX supported on brackets 58 together with the nozzles. The solenoid valves SVl, etc., are controlled over an electrical cable 60 extending to an instrument panel assembly 62 on the framework 40.

The instrument panel 62 includes a plurality of switches SW1 and Sl-SX with the latter operable for selecting the solenoid valves to be operated. The panel also includes a plurality of lamps such as 64 for indicating operation of the solenoid valves and both a timer 66 and a counter 68. The counter 68 is arranged to be operated from a pulse contact assembly 70 over an electrical cable 72 and the pulse contact assembly in turn is operated through a flexible shaft assembly 74.

The flexible shaft assembly 74 as seen in FIG. 3 comprises a conventional casing 76 encircling an elongate flexible shaft 78. Each end of the casing 76 terminates in a ferrule 80 fastened to a respective cap 82 on the contact assembly 70 and journal block 42, respectively. Cap 82 on block 42 has an opening coaxial with the axis of a shaft 84 that carries the absorbent roll 46. The corresponding end of the flexible shaft 78 passes through the cap opening.

The noncircular flexible shaft end engages in a correspondingly shaped opening of a coupling element 86 press fit into the end of the shaft 84 so that the flexible shaft 78 rotates at the same speed as the shaft 84 and the roll 46. Since the roll 46 is moved by the passing web 18, the roll 46 in turn moves at the same speed as the web 18.

The other end of the flexible shaft 78 passes through an opening in the cap 82 on the pulse contact assembly 70. The opening is coaxial with a shaft 88 of the first gear of a gear reduction assembly or gear box 90 in the pulse contact assembly 70. A connector 92 connects the respective flexible shaft end with the shaft 88 so that the gears of assembly 90 are driven at a rate corresponding to the web speed. The gears in box 90 conventionally provide a 50-to-l reduction between the input speed and output speed.

The assembly 70 comprises a U-shaped bracket 94 with a baseplate 96 straddling the legs of bracket 90 for supporting gear box 90 together with a rotatable disc 98. The disc 98 is driven by the web 18 through the roll 46, shafts 84, 78 and 88 and the gears in box 90. The disc 98 carries a plurality of magnetic switch-actuating assemblies 100 distributed adjacent the circumference of disc 98 and extending axially from the disc. In this case six assemblies 100 are provided and each is adapted to operate a pair of contacts 102 (seen in FIG. 6) of a reed switch assembly 104 supported on plate 96 as each assembly 100 rotates past the switch assembly 104. The contact assembly includes conventional arc suppression apparatus and the contacts 102 are adapted to send a pulse on each operation over leads 105 and 106 extending through cable 72 to the counter 68.

The timer 66 and the counter 68 are manufactured by D. W. Bliss Company, 736' Federal Street, Davenport, Iowa under Model Nos. HI 515.46 and H2 I72A6, respectively, and shown in bulletins 125 and 725, respectively. The timer 66 and counter 68 have a respective conventional cam Cl and C2 (FIG. 6) and each includes a stop. Both cam and stop of the timer and the counter are manually set or rotated to a desired position by a respective knob 108, seen in FIG. 5, and their position indicated on a respective dial. The cams C1 and C2 are then driven to a home position as will be explained.

The cam C1 of the timer 66 is driven to its home position whenever a timer clutch magnet 110 and a timer motor M1 are energized while the stop remains in the set position. On reaching the home position the cam C1 operates contacts CS1 and CS2 to deenergize the clutch magnet 110 and motor Ml. Deenergizing the clutch magnet 110 permits a return spring to move the cam C1 back to the position in which the stop has been set by the respective knob 108 so that the cycle may be repeated.

The counter 68 also has a clutch magnet and operates on a similar principle as the timer 66 except that a stepping magnet SM1 is used to step the cam C2 incrementally from the set position to the home position in response to pulses received over leads 105 and 106 from the pulse contacts 102. In the home position the cam C2 operates contacts CS4 to deenergize the clutch magnet 120 and a return spring then returns the cam C2 to the position in which the stop is set by the respective knob 108.

The circuit employing the timer 66 and the counter 68 for controlling the spray nozzles N1, etc., is shown in FIG 6 and generally identified by the reference character 130. The circuit includes the circuit for the timer 66 and the circuit for the counter 68 with switches Sl-SX shown for selecting the solenoids SVl-SVX and respective indicator lamps 64 to be operated. It will be understood that the switches Sl-SX are connected to control as many respective solenoid valves as desired. For example, switch S1 may control solenoids SVl, SVla, SVlb and SVlc. The solenoid valves SV] and SVla and their respective spray nozzles may be located at the opposite ends of one nozzle row and valves SVlb and SVlc in the opposite row. Similarly, switch SX may control solenoid valve SVX and SVXl in either opposite rows or at different positions in the same row. OTher switches control either intermediate pairs of solenoid valves or individual valves in each row. This enables the width of the spray to be selected for correspondence with the width of the web. It will also be appreciated that under some circumstances only one row of solenoid valves and nozzles will be used.

The circuit for timer 66 includes the clutch magnet 110, which enables the timer motor M1 to drive the timer cam C1 during the period in which solenoids SV1SVX are operated. In this type of timer the cam Cl is manually set to a desired position corresponding to the time which the sprays are to operate and the motor M1 drives the cam to its home position where it controls three sets of contacts CS1, CS2 and CS3. Thereafter, the cam C1 is reset to the desired position automatically under control of the return spring as described for the purpose of repeating the cycle.

The circuit for counter 68 comprises the clutch magnet 120 for enabling solenoid SM1 to step cam C2 incrementally through a ratchet mechanism. That is, the cam C2 is set in a position corresponding to the desired count and as the solenoid SM1 receives pulses from the pulse contacts 102, solenoid SM1 steps the cam C2 incrementally until the cam reaches its home position. On reaching the home position the cam C2 opens contacts CS4 and is reset to the set position under control of the return spring as described for the purpose of repeating the cycle.

The switches Sl-SX are manually operated for the purpose of selecting the solenoid valves SV1SVX for operation by the timer to spray the web. The selected valves depend usually on the web width so that, for example, if a web of small width is to oiled, only solenoids adjacent the center of the solenoid valve and nozzle row are operated by closure of the corresponding switch, while if it is desired to operate all sprays all of the switches Sl-SX are operated.

Briefly, the operation of the circuit is as follows. The switch SW1 is operated to connect power through normally closed cam contacts CS4, counter clutch magnet contacts 124, to the clutch magnet 110 and the timer motor M1, the latter being in shunt with indicator lamp LM, which lights to indicate the timer is operated.

The clutch magnet 110 closes contacts 112 so that power is applied directly from switch SW1 through contacts CS1 to the timer motor M1 and magnet 110. Contacts 114 are also closed by magnet 110 so that power is applied from cam contacts CS3 through the operated ones of switches SlSX to the respective solenoid valves SVl-SVX in shunt with respective indicator lamps 64 to indicate the operated solenoids. The operated ones of solenoid valves SVl-SVX open the oil supply to respective spray nozzles and oil is delivered to the absorbent roll 46 and applied to the web 18 to provide an oil coating initially to the web.

The timer cam C1 in the meantime is driven by the motor Ml towards the timer home position and when the cam Cl reaches the same it opens contacts CS1 and CS3 and closes contacts CS2 before contacts CS1 open. Opening contacts CS1 opens one circuit to the motor M1 and opening contacts CS3 deenergizes the spray solenoids SVl-SVX.

Closing contacts CS2 extends power from switch SW1 to clutch magnet 120 in shunt with indicator lamp LP which indicates the counter is in operation. Clutch magnet 120 opens contacts 124 to open the original circuit to magnet 110 and motor M1 to deenergize the clutch magnet 110 and motor Ml as soon as contacts CS1 open. The cam C1 resets under control of the return spring to open contacts CS2 and close contacts CS1 and CS3; however, since contacts 124 are open, the magnet 110 and motor M1 do not reenergize at this time. The spray solenoid valves SVl-SVX also do not reenergize, since contacts 114 are open. Magnet 120 in the meantime stays energized over a holding circuit through contacts 122 and CS4 to prevent closure of contacts 124 and reenergization of magnet 110 and motor M1.

Power from switch SW1, contacts CS4 and 122 is now extended to the stepping magnet SMl each time contacts 102 close in response to each passage of one of the magnet assemblies 100 past the switch assembly 104, The magnet 8M1 steps the cam C2 once for each pulse. The pulse contacts 102 close at time intervals dependent on the web speed as it passes the coating roll 46. Since the web length which rotates the roll 46 an increment or angular distance necessary to operate contacts 102 is constant, the number of pulses necessary to step cam C2 home is independent of the web speed. A predetermined web length, therefore, passes the roll 46 in order to step cam C2 to its home position irrespective of changes in web speed.

When cam C2 reaches its home position contacts CS4 open to deenergize the clutch magnet 120 and the lamp LP. Clutch magnet 120 opens contacts 122 to prevent its further energization or further energization of the steppingfimagnet 120 and closes contacts 124. The cam C2 returns to its set position under influence of the return spring and contacts CS4 close to reenergize the clutch magnet 110 and the timer motor over contacts 124 as previously explained.

Thereafter the cycle of timed spray is repeated with the counter 68 prevented from operating as explained until the timer motor M1 steps cam C1 to its home position. The counter is then again rendered effective and it counts out a' total predetermined web length as previously explained, whereafter the timer is again rendered ineffective.

The off time is thus independent of the speed at which the web is traveling and since the web length that passes roll 46 usually constitutes the major portion of the web length for the entire cycle, the thickness of the coating is maintained relatively constant irrespective of web speed.

It will be appreciated that the spray time remains constant unless altered by the operator and, therefore, the total web length passing the roll for each spray cycle will depend on both the count and the spray time. The web length passing during the count cycle is constant and since the greater portion of the web passes during the count cycle any changes in web speed are reflected only to a relatively small degree by changes in web length over the entire spray cycle. This change is relatively small as may be seen from the following figures. If the web is traveling at 4,000 feet per minute, to rotate an 8- inch-diameter roll at somewhat less than 2,000 rpm, the six switch-actuating assemblies will make less than one revolution per two-thirds of a second with a 50-to-l gear reduction. With the counter 68 set for eight counts, the dry cycle is approximately 1 second and 66 feet of web passes the roll 46 during the dry cycle, while a typical spray time is onethird second during which 22 feet of web pass the roll. A total of approximately 88 feet pass the roll in one full cycle. Now, if the web speed falls to as low as 2,000 feet per minute, the web length passing the counter is constant at 66 feet but only 11 feet of web passes during the one-third second spray cycle. This reduces the total web length in the cycle to 77 feet; however, this is a relatively small reduction as compared with the total length per cycle and due to the characteristics of the absorbent roll the coating thickness will remain relatively constant.

lf, on the other hand, the web is moving at 2,000 feet per minute, the switch assemblies are rotating at approximately one revolution per 1 ilseconds. With the counter 68 set for 12 counts, approximately 88 feet of web pass during the dry portion of the cycle. With the spray cycle set for two-thirds of a second about 22 additional feet of web passes. Now, if the web speed increases to 4,000 feet per minute or 66 feet per second, there will still be 88 feet of web passing during the dry cycle and approximately 44 feet of web during the spray cycle so that the variation in total web length is only 22 feet per total cycle even if the web speed doubles. By operating the counter only when the spray cycle is off and by rendering the dry portion of the cycle relatively long and constant, a selected uniform coating thickness is provided over a relatively large range of web speeds.

In the described system either the spray cycle or the dry cycle may be varied as desired. Thus, the timer may provide up to l0 seconds of spray time in one-third ofa second increments, and the counter may provide up to 40 counts before energizing the timer so that an extremely wide range of coating thicknesses can be provided under a large variety of conditions.

The foregoing constitutes a description of one embodiment of a web coating system or method whose inventive concepts are believed set forth in the accompanying claims.

What I claim is:

1. Apparatus for spraying oil on an absorbent roll engaged with a moving web to provide a uniform coating of oil having a selected thickness on said web in response to the application of an oil spray to said roll, the improvement comprising a counter, means rotated in response to the movement of said web for repeatedly operating said counter to detect the passage of a predetermined web length, a timer operable for a selected time period, means operated in response to said counter detecting the passage of said predetermined web length for operating said timer and for spraying said oil on said roll only for said selected time period under control of said timer, means operated in response to said counter detecting said predetermined web length for disabling said counter for said selected time period, and means operated in response to the operation of said timer for said selected time period for thereafter enabling operation of said counter and for preventing operation of said timer until said counter again detects said predetermined web length.

2. The apparatus claimed in claim 1 in which said counter is adjustable to select a desired number of said predetermined web lengths, and said timer is adjustable to select any one of a plurality of different time periods with the portion of the web passing said roll during any one of said selected time periods being shorter than the total of said predetermined web lengths.

3. Apparatus for spraying oil on an absorbent roll engaged with a moving web for rotation in response to the movement of said web to provide a uniform coating of oil having a selected thickness on said web in response to the application of an oil spray to said roll, the improvement comprising a counter, means rotated in synchronism with the rotation of said roll for periodically operating said counter to count the passage of each of a plurality of predetermined web "lengths each corresponding to a predetermined angular distance traveled by said roll, an adjustable timer operable for a selected time period, means operated in response to said counter operating said selected plurality of times for operating said timer and for spraying said oil on said roll only for said selected time period under control of said timer, means operated in response to said counter being operated said selected plurality of times for preventing operation of said counter for said selected time period, and means operated in response to the operation of said timer for said selected time period for thereafter enabling operation of said counter and for preventing operation of said timer until said counter is again operated for said selected plurality of times.

'4. Apparatus for spraying a liquid on an absorbent roll engaged with a moving web to provide a uniform coating of liquid having a selected thickness on said web in response to the application of a liquid spray to said roll, the improvement comprising means for detecting the passage of a predetermined length of said web irrespective of variations in the speed of said web, clock means operable for a predetermined time in response to the detection of the passage of said predetermined web length by said detecting means for enabling the application of said liquid spray and for disabling said detecting means for said predetermined time period, and means operated in response to the termination of the operation of clock means at the end of said time period for enabling said detecting means and terminating said liquid spray. 

1. Apparatus for spraying oil on an absorbent roll engaged with a moving web to provide a uniform coating of oil having a selected thickness on said web in response to the application of an oil spray to said roll, the improvement comprising a counter, means rotated in response to the movement of said web for repeatedly operating said counter to detect the passage of a predetermined web length, a timer operable for a selected time period, means operated in response to said counter detecting the passage of said predetermined web length for operating said timer and for spraying said oil on said roll only for said selected time period under control of said timer, means operated in response to said counter detecting said predetermined web length for disabling said counter for said selected time period, and means operated in response to the operation of said timer for said selected time period for thereafter enabling operation of said counter and for preventing operation of said timer until said counter again detects said predetermined web length.
 2. The apparatus claimed in claim 1 in which said counter is adjustable to select a desired number of said predetermined web lengths, and said timer is adjustable to select any one of a plurality of different time periods with the portion of the web passing said roll during any one of said selected time periods being shorter than the total of said predetermined web lengths.
 3. Apparatus for spraying oil on an absorbent roll engaged with a moving web for rotation in response to the movement of said web to provide a uniform coating of oil having a selected thickness on said web in response to the application of an oil spray to said roll, the improvement comprising a counter, means rotated in synchronism with the rotation of said roll for periodically operating said counter to count the passage of each of a plurality of predetermined web lengths each corresponding to a predetermined angular distance traveled by said roll, an adjustable timer operable for a selected time period, means operated in response to said counter operating said selected plurality of times for operating said timer and for spraying said oil on said roll only for said selected time period under control of said timer, means operated in response to said counter being operated said selected plurality of times for preventing operation of said counter for said selected time period, and means operated in response to the operation of said timer for said selected time period for thereafter enabling operation of said counter and for preventing operation of said timer until said counter is again operated for said selected plurality of times.
 4. Apparatus for spraying a liquid on an absorbent roll engaged with a moving web to provide a uniform coating of liquid having a selected thickness on said web in response to the application of a liquid spray to said roll, the improvement comprising means for detecting the passage of a predetermined length of said web irrespective of variations in the speed of said web, clock means operable for a predetermined time in response to the detection of the passage of said predetermined web length by said detecting means for enabling the application of said liquid spray and for disabling said detecting means for said predetermined time period, and means operated in response to the termination of the operation of clock means at the end of said time period for enabling said detecting means and terminating said liquid spray. 